Unit 3 Flashcards
What are the 2 levels of bacterial growth
Cellular growth
Replication
Cellular growth of bacteria
Increasing mass at the cellular level (in preparation to divide)
Makes new cell components (proteins, cytoplasm, cell wall, DNA)
Replication in bacterial growth
Increasing mass at the population level
The number is cells increase exponentially due to binary fission
Binary fission
How bacteria replicate: one bacteria divides into 2 identical daughter cells
2 stages:
Replication of cellular components
Separation into two equal and identical halves by forming a septum in the middle of the cell
Generation time (AKA doubling time)
Time required for one round of binary fission (amount of time to double the number of bacteria)
What does the generation time depend on
Environment: growth factors, temp, oxygen, nutrients etc
Exponential (log) growth
The number of bacteria or population size doubles every generation
Equation:
N(total)=(Ni) 2^n
N= population n= generation
Bacterial growth curve is observed when
Microorganisms are grown in a culture in a closed system (limited space and nutrients)
What are the 4 phases of the bacterial growth curve
Lag phase
Exponential/log phase
Stationary phase
Senescence/death phase
What is the lag phase
Period of adjustments after cells are inoculated into fresh media
Very slow growth
What happens during the lag phase
Cells adapt to new conditions
Cells repair, and replenish spent materials
Increase in size due to synthesis of DNA and proteins
Minimal cell division
Varies in length (short, long or absent)
What is the exponential phase?
AKA log or logarithmic phase
Bacteria have acclimated and conditions are now optimal for growth (excess nutrients, space, lack of toxins)
Rapid growth (consistently doubles)
Why is the log phase clinically significant? (2)
Population is most uniform (chemical and physical properties): best time to identify bacteria
Bacteria in this phase are MOST susceptible to antibiotics
Why are bacteria most susceptible to antibiotics during the log phase
Because antibiotics often target a stage in binary fission
What is the stationary phase
Rate of replication equals rate of death
Overall number of bacteria stays constant
Occurs when growing conditions are no longer ideal
Less susceptible to antibiotics here
What is the senescence/death phase
Rate of cell death exceed rate of growth
Rapid decline in numbers of viable bacteria
Majority of cells die by autolysis
Autolysis
Expression of specific self-digestion Genes
Dormancy (metabolically inactive) bacteria is a response to what
Potential or actual change in environment, when it becomes unfavourable
What makes an environment unfavourable
Lack of nutrients Lack of spaces Increased waste Change in oxygen Change in temp Presence of antibiotics
Examples of dormant states of bacteria
Persister cells
Endospores
What are persister cells
Small number of cells in a population that are slow or non growing
When environmental conditions improve, they reestablish population/reinfect
Persister cells are more ____ to kill with antibiotics
Difficult
Persister cells hide out in macrophages, and can survive through antibiotic treatment, to
Re infect
What are endospores
A dormant, tough, non reproductive structure in bacteria (gram positive)
Production Triggered by lack of nutrients (starvation)
Resistant to dry conditions/heat
Difficult to eliminate
Bacillus and clostridium produce these
Why is it important to know which phase of growth bacteria are in?
Bacteria can be identified best in the log phase
Bacteria are most vulnerable to harm in the log phase
Cells are more difficult to treat and identify in stationary phase
Stages of growth correspond to stages of infection
Physical and chemical requirements for growth
Temperature Oxygen levels PH Moisture Osmotic pressure Space
Temperate affects
Rate and amount of growth
Minimum temperature
Lowest temperature that growth will occurs
Less than minimum will inhibit growth
Optimal temperature
Growth is maximal
Ex. Incubator temperatures
Maximum temperature
Highest temperature at which growth will occur
If exceeded, denaturation will occur
Most clinically relevant species are mesophiles, their range of temperature is
20-45 degrees Celsius
Fever
A Mechanism the body uses to decrease microbial growth during infection
The ability to withstand low and high temperatures would be considered a
Pathogenic factor
Ideal temperatures for: psychrophile
0-20 degrees Celsius
Ideal temperatures for: psychrotrophs
0-30 degrees Celsius
15 degrees is optimal
Ideal temperatures for: mesophile
20-45 degrees Celsius
Ideal temperatures for: thermophiles
45-85 degrees Celsius
Ideal temperatures for: thermoduric
Able to withstand high temp but do not grow at them, can survive pasteurization, including spores
Bacteria require certain amounts of oxygen for growth depending on
The type of metabolic enzymes they express
Bacteria that produce energy via oxidative phosphorylation and the electron transport chain
Require oxygen
Bacteria that produce energy via fermentation
Do not require oxygen
Aerobes
Grown in 21% oxygen
Obligate aerobes
Can’t grow without oxygen
Facultative anaerobe
Grown best in aerobic conditions but can grow in absence of oxygen
(Intestinal bacteria)
Obligate anaerobe
Cannot grow if exposed to oxygen
Microaerophile
Grow in 2-10% oxygen
Some bacteria can alter their environments pH, how does E. Coli do this
Frequent cause of UTIs
Produces urease: an enzyme that converts urea to ammonia and CO2 to bring urine closer to ideal pH
Urine is slightly acidic, E.Coli has an optimal growth at pH of 7
Optimal pH range for: acidophils
pH 4 (0-5.5)
Optimal pH range for: neutrophils
pH 7.2 (5.5-8.5)
Optimal pH range for: alkaliphils
pH 9 (8.5-11.5)
Bacteria are made up of 70% water
So moisture is
Necessary for growth
Osmotic pressure is
Difference in solute concentration between the inside of the bacteria cell and external environment
Isotonic
No water movement
Hypotonic
Less solutes outside the cell, more solutes inside the cell
Water moves into the cell, cell swells and bursts (lysis due to osmotic pressure)
Cell wall protects from osmotic lysis
Hypertonic
Water moves out of the cell causing shrinkage (dehydration) (plasmolysis)
More solutes outside the cell
Why do bacteria need room to grow?
Space allows toxic metabolic waste to diffuse out
Normal intestinal flora are important in maintaining health by
Occupying space and preventing pathogenic bacteria from finding space to grow
Metabolism: catabolism
Process of energy production
Energy is released by breaking down large molecules into smaller ones
Metabolism: anabolism
Energy requiring processes
Energy is used to build molecules for growth and repair
Heterotrophs
An organism that eats other plants or organisms for energy
Require pre-formed organic matter for energy and carbon needs (must be supplied)
Why are bacteria more versatile than mammals in terms of nutrition?
Bacteria can utilize a wider range of nutrients including inorganic sources of carbon and other elements
Macronutrients
Nutritional elements required in relatively large amounts by all living organisms
Main macronutrients
Carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus
True or false
Some bacteria can obtain carbon, nitrogen and sulfur from inorganic sources
True
Other macronutrients need in lesser amounts
Potassium, calcium, sodium, magnesium, iron
Needed for proper function of enzymes and to maintain osmolarity
Micronutrients
AKA trace elements
Only very small amounts required
Involved as co-factors in enzyme function and protein structure
Examples of micronutrients
Manganese, zinc, Cobalt, Molybdenum, nickel, copper
Essential nutrients are
Any nutritional component that has to be provided to the cell/organism because it is unable to produce it on its own
Usually taken from the host
Bacteria have Different nutritional requirements based on the
Metabolic enzymes they have genes for
Why must you know nutritional differences when growing bacteria in vitro
Can use to differentiate between different species
